There are legends about Fuxi, who in the beginning used turtles (according to some stories, it must have been a sacred white turtle) for I Ching divination. So, in the end of Shang Dynasty in China it was quite popular to use turtle shells for divination. Many people killed the turtles in a very cruel way, for divination purposes. While the turtle was still alive, the diviners pressed it above with a heavy stone, then they heated the turtle from its tail in order to let her leave the shell. The heat caused some cracks on the shell and the newly formed cracks and signs were interpreted (according to the direction of the cracks, etc.).
In the next dynasty, Zhou dynasty, the people started replacing turtle shells for yarrow stalks for I Ching divination. So this was a change for better, more humane way of divination. The ancient people regarded the yarrow as a supernatural herb, which can live for thousands of years. There are many records in the ancient books about this. For example, in the treatise “Wan Xing Jing” 《万行经》, it is said:
“The yarrow lives for thousand of years. When it is 100 years, it has 49 stems, which completely corresponds to the numbers of Heaven and Earth.
When the yarrow achieves 500 years, it gradually starts to dry and solidify.
When it achieves 700 years, it is without branches and leaves.
When the yarrow achieves 900 years, its color is purple as iron.
At the age of 1000 years, it attains a purple energy and below it there concedes a sacred turtle”.
In another book, Xuan Yuan Mu Jing 《轩辕木经》, it is said:
“Under the purple yarrow, there are five dragons hiding. It has a naturally born sensitivity. If gathered by the sages and 49 sticks are used, thus applying the numbers of Heaven and Earth, it [connects to] all origins [of things]”.
Mentioning the numbers of Heaven and Earth, usually in yarrow divination there are used 49 or 50 sticks. However, there was a Taoist who told me that 55 sticks of yarrow should be used in the initial stage of the I Ching divination ritual. The Heaven numbers (1+3+5+7+9) + the Earth numbers (2+4+6+8+10) = 55. From these 55 sticks you get aside 6 sticks (as a part of the ritual). Those 6 stalks of yarrow represent the person (as part of the connections Heaven-Man-Earth).
If the yarrow grows in spiritual and mountainous places, full of energy, then this yarrow is regarded of best quality. If it grows next to the road or on a common field, it has lesser properties.
In Records on the Yarrow Platform 《蓍草台记》, written by Yang Xun of Ming Dynasty, it is written "the head (the stalk) of the yarrow is as strong as a dragon; its tail (flowers) is like the wings of the phoenix”. This book actually describes a place in Henan province, where there is a famous Yarrow Garden with a platform of the eight trigrams. According to the legends, there live a rare species of white turtles…